1. Field of the Invention
This invention relates to an airbag for use in a vehicle occupant restraint system and more particularly, to an airbag whose inflation state is controlled by controlling gas flow of the inflator by means of an internal cloth enclosed within the airbag proper.
2. Statement of Related Art
As airbags of the type as stated above, for example, an airbag is known and disclosed in Japanese U.M. Laid-open Publication 2-71052 (1990), which comprises two circular cloths on an inflator side and an occupant side superposed and seamed together at respective outer peripheral portions thereof to form an external configuration of the airbag, the inflator side cloth having a central opening through which to insert the head part of the inflator, and an inside cloth, of substantially the same radius as the two cloths, interposed between the inflator side cloth and the occupant side cloth and seamed at its outer peripheral portion to both cloths. The inside cloth is formed discontinuously with cutouts at its outer periphery and seamed to the inflator side cloth further at its radially middle positions between the center point and the outer perimeter, the middle positions being located at intervals along the perimetric portions where the cutouts are not formed.
With the airbag thus constructed, gas released from the inflator strikes the inside cloth to flow in radial directions toward the outer peripheral portion of the airbag and further passes through the cutouts to inflate the airbag in a flat flaring shape.
However, the foregoing airbag is disadvantageous in the aspects of cost and manufacturing procedure since the inside cloth is of a large size and fashioned in a complicated shape because of the formation of the cutouts, and sewing must be applied in the intermediate positions as well as the outer peripheral portions. A further problem with the airbag is that vent holes are formed in the inflator side cloth in a range in which the inside cloth is attached to because of the large size of the inside cloth and consequently, gas from the inflator strikes the inside cloth and is escaped out of the vent holes in the course of inflation of the airbag.
Another airbag restraint system for a motor vehicle is disclosed in Japanese Patent Publication 53-45574 (1978), according to which the airbag has therein an insert that is automatically inflatable by the gas in the event that a deceleration of the vehicle exceeding over a predetermined speed takes place and, upon inflation by the gas, is thrusted out in a parachute form in a major flow direction of the gas from its housing position within the airbag.
This is only aimed at diminishing the generation of sound when the airbag is inflated so that it does no harm to the human body, and no control of flow of the inflator gas is taken into account and pursued.
Another airbag is proposed in Japanese Patent Laid-open Publication 3-281460 (1991), which is constructed of a small-volume inner bag housed in a large-volume outer bag so that inflation gas pressure may be supplied through the inner bag to the outer bag. However, the inner bag itself must have holes for passage of the gas because of restriction by its bag shape, and fabrication of the airbag entails a laborious task and a cost increase.
Further, German Patent Laid-open Publication (DEOS) 41 21 659 A1 discloses an airbag within which a covering is provided over the opening of the inflator side cloth. The covering has a plurality of holes for passage of gas, which not only causes a reduction in strength, but also allows a main flow of the gas to pass through the holes and to flow direct into the airbag. Consequently, the airbag is not satisfactory for the control of gas flow.
In view of the defects or problems as described above, this invention has been accomplished, and its general object is to provide an improved airbag capable of controlling the gas flow of the inflator and suppressing the escape of the gas out of vent holes by another construction of an inside cloth.
Further object is to manufacture the airbag at low cost and in easier process steps.